# Django 2.0.dev20170216164632 documentation

# Source code for django.forms.models

    """
    Helper functions for creating Form classes from Django models
    and database field objects.
    """

    from collections import OrderedDict
    from itertools import chain

    from django.core.exceptions import (
        NON_FIELD_ERRORS, FieldError, ImproperlyConfigured, ValidationError,
    )
    from django.forms.fields import ChoiceField, Field
    from django.forms.forms import BaseForm, DeclarativeFieldsMetaclass
    from django.forms.formsets import BaseFormSet, formset_factory
    from django.forms.utils import ErrorList
    from django.forms.widgets import (
        HiddenInput, MultipleHiddenInput, SelectMultiple,
    )
    from django.utils.encoding import force_text
    from django.utils.text import capfirst, get_text_list
    from django.utils.translation import gettext, gettext_lazy as _

    __all__ = (
        'ModelForm', 'BaseModelForm', 'model_to_dict', 'fields_for_model',
        'ModelChoiceField', 'ModelMultipleChoiceField', 'ALL_FIELDS',
        'BaseModelFormSet', 'modelformset_factory', 'BaseInlineFormSet',
        'inlineformset_factory', 'modelform_factory',
    )

    ALL_FIELDS = '__all__'

    def construct_instance(form, instance, fields=None, exclude=None):
        """
        Constructs and returns a model instance from the bound ``form``'s
        ``cleaned_data``, but does not save the returned instance to the
        database.
        """
        from django.db import models
        opts = instance._meta

        cleaned_data = form.cleaned_data
        file_field_list = []
        for f in opts.fields:
            if not f.editable or isinstance(f, models.AutoField) \
                    or f.name not in cleaned_data:
                continue
            if fields is not None and f.name not in fields:
                continue
            if exclude and f.name in exclude:
                continue
            # Leave defaults for fields that aren't in POST data, except for
            # checkbox inputs because they don't appear in POST data if not checked.
            if (f.has_default() and
                    form[f.name].field.widget.value_omitted_from_data(form.data, form.files, form.add_prefix(f.name))):
                continue
            # Defer saving file-type fields until after the other fields, so a
            # callable upload_to can use the values from other fields.
            if isinstance(f, models.FileField):
                file_field_list.append(f)
            else:
                f.save_form_data(instance, cleaned_data[f.name])

        for f in file_field_list:
            f.save_form_data(instance, cleaned_data[f.name])

        return instance

    # ModelForms #################################################################

    def model_to_dict(instance, fields=None, exclude=None):
        """
        Returns a dict containing the data in ``instance`` suitable for passing as
        a Form's ``initial`` keyword argument.

        ``fields`` is an optional list of field names. If provided, only the named
        fields will be included in the returned dict.

        ``exclude`` is an optional list of field names. If provided, the named
        fields will be excluded from the returned dict, even if they are listed in
        the ``fields`` argument.
        """
        opts = instance._meta
        data = {}
        for f in chain(opts.concrete_fields, opts.private_fields, opts.many_to_many):
            if not getattr(f, 'editable', False):
                continue
            if fields and f.name not in fields:
                continue
            if exclude and f.name in exclude:
                continue
            data[f.name] = f.value_from_object(instance)
        return data

    def fields_for_model(model, fields=None, exclude=None, widgets=None,
                         formfield_callback=None, localized_fields=None,
                         labels=None, help_texts=None, error_messages=None,
                         field_classes=None):
        """
        Returns a ``OrderedDict`` containing form fields for the given model.

        ``fields`` is an optional list of field names. If provided, only the named
        fields will be included in the returned fields.

        ``exclude`` is an optional list of field names. If provided, the named
        fields will be excluded from the returned fields, even if they are listed
        in the ``fields`` argument.

        ``widgets`` is a dictionary of model field names mapped to a widget.

        ``formfield_callback`` is a callable that takes a model field and returns
        a form field.

        ``localized_fields`` is a list of names of fields which should be localized.

        ``labels`` is a dictionary of model field names mapped to a label.

        ``help_texts`` is a dictionary of model field names mapped to a help text.

        ``error_messages`` is a dictionary of model field names mapped to a
        dictionary of error messages.

        ``field_classes`` is a dictionary of model field names mapped to a form
        field class.
        """
        field_list = []
        ignored = []
        opts = model._meta
        # Avoid circular import
        from django.db.models.fields import Field as ModelField
        sortable_private_fields = [f for f in opts.private_fields if isinstance(f, ModelField)]
        for f in sorted(chain(opts.concrete_fields, sortable_private_fields, opts.many_to_many)):
            if not getattr(f, 'editable', False):
                if (fields is not None and f.name in fields and
                        (exclude is None or f.name not in exclude)):
                    raise FieldError(
                        "'%s' cannot be specified for %s model form as it is a non-editable field" % (
                            f.name, model.__name__)
                    )
                continue
            if fields is not None and f.name not in fields:
                continue
            if exclude and f.name in exclude:
                continue

            kwargs = {}
            if widgets and f.name in widgets:
                kwargs['widget'] = widgets[f.name]
            if localized_fields == ALL_FIELDS or (localized_fields and f.name in localized_fields):
                kwargs['localize'] = True
            if labels and f.name in labels:
                kwargs['label'] = labels[f.name]
            if help_texts and f.name in help_texts:
                kwargs['help_text'] = help_texts[f.name]
            if error_messages and f.name in error_messages:
                kwargs['error_messages'] = error_messages[f.name]
            if field_classes and f.name in field_classes:
                kwargs['form_class'] = field_classes[f.name]

            if formfield_callback is None:
                formfield = f.formfield(**kwargs)
            elif not callable(formfield_callback):
                raise TypeError('formfield_callback must be a function or callable')
            else:
                formfield = formfield_callback(f, **kwargs)

            if formfield:
                # Apply ``limit_choices_to``.
                if hasattr(formfield, 'queryset') and hasattr(formfield, 'get_limit_choices_to'):
                    limit_choices_to = formfield.get_limit_choices_to()
                    if limit_choices_to is not None:
                        formfield.queryset = formfield.queryset.complex_filter(limit_choices_to)
                field_list.append((f.name, formfield))
            else:
                ignored.append(f.name)
        field_dict = OrderedDict(field_list)
        if fields:
            field_dict = OrderedDict(
                [(f, field_dict.get(f)) for f in fields
                    if ((not exclude) or (exclude and f not in exclude)) and (f not in ignored)]
            )
        return field_dict

    class ModelFormOptions:
        def __init__(self, options=None):
            self.model = getattr(options, 'model', None)
            self.fields = getattr(options, 'fields', None)
            self.exclude = getattr(options, 'exclude', None)
            self.widgets = getattr(options, 'widgets', None)
            self.localized_fields = getattr(options, 'localized_fields', None)
            self.labels = getattr(options, 'labels', None)
            self.help_texts = getattr(options, 'help_texts', None)
            self.error_messages = getattr(options, 'error_messages', None)
            self.field_classes = getattr(options, 'field_classes', None)

    class ModelFormMetaclass(DeclarativeFieldsMetaclass):
        def __new__(mcs, name, bases, attrs):
            base_formfield_callback = None
            for b in bases:
                if hasattr(b, 'Meta') and hasattr(b.Meta, 'formfield_callback'):
                    base_formfield_callback = b.Meta.formfield_callback
                    break

            formfield_callback = attrs.pop('formfield_callback', base_formfield_callback)

            new_class = super(ModelFormMetaclass, mcs).__new__(mcs, name, bases, attrs)

            if bases == (BaseModelForm,):
                return new_class

            opts = new_class._meta = ModelFormOptions(getattr(new_class, 'Meta', None))

            # We check if a string was passed to `fields` or `exclude`,
            # which is likely to be a mistake where the user typed ('foo') instead
            # of ('foo',)
            for opt in ['fields', 'exclude', 'localized_fields']:
                value = getattr(opts, opt)
                if isinstance(value, str) and value != ALL_FIELDS:
                    msg = ("%(model)s.Meta.%(opt)s cannot be a string. "
                           "Did you mean to type: ('%(value)s',)?" % {
                               'model': new_class.__name__,
                               'opt': opt,
                               'value': value,
                           })
                    raise TypeError(msg)

            if opts.model:
                # If a model is defined, extract form fields from it.
                if opts.fields is None and opts.exclude is None:
                    raise ImproperlyConfigured(
                        "Creating a ModelForm without either the 'fields' attribute "
                        "or the 'exclude' attribute is prohibited; form %s "
                        "needs updating." % name
                    )

                if opts.fields == ALL_FIELDS:
                    # Sentinel for fields_for_model to indicate "get the list of
                    # fields from the model"
                    opts.fields = None

                fields = fields_for_model(opts.model, opts.fields, opts.exclude,
                                          opts.widgets, formfield_callback,
                                          opts.localized_fields, opts.labels,
                                          opts.help_texts, opts.error_messages,
                                          opts.field_classes)

                # make sure opts.fields doesn't specify an invalid field
                none_model_fields = [k for k, v in fields.items() if not v]
                missing_fields = (set(none_model_fields) -
                                  set(new_class.declared_fields.keys()))
                if missing_fields:
                    message = 'Unknown field(s) (%s) specified for %s'
                    message = message % (', '.join(missing_fields),
                                         opts.model.__name__)
                    raise FieldError(message)
                # Override default model fields with any custom declared ones
                # (plus, include all the other declared fields).
                fields.update(new_class.declared_fields)
            else:
                fields = new_class.declared_fields

            new_class.base_fields = fields

            return new_class

    class BaseModelForm(BaseForm):
        def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
                     initial=None, error_class=ErrorList, label_suffix=None,
                     empty_permitted=False, instance=None, use_required_attribute=None):
            opts = self._meta
            if opts.model is None:
                raise ValueError('ModelForm has no model class specified.')
            if instance is None:
                # if we didn't get an instance, instantiate a new one
                self.instance = opts.model()
                object_data = {}
            else:
                self.instance = instance
                object_data = model_to_dict(instance, opts.fields, opts.exclude)
            # if initial was provided, it should override the values from instance
            if initial is not None:
                object_data.update(initial)
            # self._validate_unique will be set to True by BaseModelForm.clean().
            # It is False by default so overriding self.clean() and failing to call
            # super will stop validate_unique from being called.
            self._validate_unique = False
            super().__init__(
                data, files, auto_id, prefix, object_data, error_class,
                label_suffix, empty_permitted, use_required_attribute=use_required_attribute,
            )

        def _get_validation_exclusions(self):
            """
            For backwards-compatibility, several types of fields need to be
            excluded from model validation. See the following tickets for
            details: #12507, #12521, #12553
            """
            exclude = []
            # Build up a list of fields that should be excluded from model field
            # validation and unique checks.
            for f in self.instance._meta.fields:
                field = f.name
                # Exclude fields that aren't on the form. The developer may be
                # adding these values to the model after form validation.
                if field not in self.fields:
                    exclude.append(f.name)

                # Don't perform model validation on fields that were defined
                # manually on the form and excluded via the ModelForm's Meta
                # class. See #12901.
                elif self._meta.fields and field not in self._meta.fields:
                    exclude.append(f.name)
                elif self._meta.exclude and field in self._meta.exclude:
                    exclude.append(f.name)

                # Exclude fields that failed form validation. There's no need for
                # the model fields to validate them as well.
                elif field in self._errors.keys():
                    exclude.append(f.name)

                # Exclude empty fields that are not required by the form, if the
                # underlying model field is required. This keeps the model field
                # from raising a required error. Note: don't exclude the field from
                # validation if the model field allows blanks. If it does, the blank
                # value may be included in a unique check, so cannot be excluded
                # from validation.
                else:
                    form_field = self.fields[field]
                    field_value = self.cleaned_data.get(field)
                    if not f.blank and not form_field.required and field_value in form_field.empty_values:
                        exclude.append(f.name)
            return exclude

        def clean(self):
            self._validate_unique = True
            return self.cleaned_data

        def _update_errors(self, errors):
            # Override any validation error messages defined at the model level
            # with those defined at the form level.
            opts = self._meta

            # Allow the model generated by construct_instance() to raise
            # ValidationError and have them handled in the same way as others.
            if hasattr(errors, 'error_dict'):
                error_dict = errors.error_dict
            else:
                error_dict = {NON_FIELD_ERRORS: errors}

            for field, messages in error_dict.items():
                if (field == NON_FIELD_ERRORS and opts.error_messages and
                        NON_FIELD_ERRORS in opts.error_messages):
                    error_messages = opts.error_messages[NON_FIELD_ERRORS]
                elif field in self.fields:
                    error_messages = self.fields[field].error_messages
                else:
                    continue

                for message in messages:
                    if (isinstance(message, ValidationError) and
                            message.code in error_messages):
                        message.message = error_messages[message.code]

            self.add_error(None, errors)

        def _post_clean(self):
            opts = self._meta

            exclude = self._get_validation_exclusions()

            # Foreign Keys being used to represent inline relationships
            # are excluded from basic field value validation. This is for two
            # reasons: firstly, the value may not be supplied (#12507; the
            # case of providing new values to the admin); secondly the
            # object being referred to may not yet fully exist (#12749).
            # However, these fields *must* be included in uniqueness checks,
            # so this can't be part of _get_validation_exclusions().
            for name, field in self.fields.items():
                if isinstance(field, InlineForeignKeyField):
                    exclude.append(name)

            try:
                self.instance = construct_instance(self, self.instance, opts.fields, opts.exclude)
            except ValidationError as e:
                self._update_errors(e)

            try:
                self.instance.full_clean(exclude=exclude, validate_unique=False)
            except ValidationError as e:
                self._update_errors(e)

            # Validate uniqueness if needed.
            if self._validate_unique:
                self.validate_unique()

        def validate_unique(self):
            """
            Calls the instance's validate_unique() method and updates the form's
            validation errors if any were raised.
            """
            exclude = self._get_validation_exclusions()
            try:
                self.instance.validate_unique(exclude=exclude)
            except ValidationError as e:
                self._update_errors(e)

        def _save_m2m(self):
            """
            Save the many-to-many fields and generic relations for this form.
            """
            cleaned_data = self.cleaned_data
            exclude = self._meta.exclude
            fields = self._meta.fields
            opts = self.instance._meta
            # Note that for historical reasons we want to include also
            # private_fields here. (GenericRelation was previously a fake
            # m2m field).
            for f in chain(opts.many_to_many, opts.private_fields):
                if not hasattr(f, 'save_form_data'):
                    continue
                if fields and f.name not in fields:
                    continue
                if exclude and f.name in exclude:
                    continue
                if f.name in cleaned_data:
                    f.save_form_data(self.instance, cleaned_data[f.name])

        def save(self, commit=True):
            """
            Save this form's self.instance object if commit=True. Otherwise, add
            a save_m2m() method to the form which can be called after the instance
            is saved manually at a later time. Return the model instance.
            """
            if self.errors:
                raise ValueError(
                    "The %s could not be %s because the data didn't validate." % (
                        self.instance._meta.object_name,
                        'created' if self.instance._state.adding else 'changed',
                    )
                )
            if commit:
                # If committing, save the instance and the m2m data immediately.
                self.instance.save()
                self._save_m2m()
            else:
                # If not committing, add a method to the form to allow deferred
                # saving of m2m data.
                self.save_m2m = self._save_m2m
            return self.instance

        save.alters_data = True

    class ModelForm(BaseModelForm, metaclass=ModelFormMetaclass):
        pass

    def modelform_factory(model, form=ModelForm, fields=None, exclude=None,
                          formfield_callback=None, widgets=None, localized_fields=None,
                          labels=None, help_texts=None, error_messages=None,
                          field_classes=None):
        """
        Returns a ModelForm containing form fields for the given model.

        ``fields`` is an optional list of field names. If provided, only the named
        fields will be included in the returned fields. If omitted or '__all__',
        all fields will be used.

        ``exclude`` is an optional list of field names. If provided, the named
        fields will be excluded from the returned fields, even if they are listed
        in the ``fields`` argument.

        ``widgets`` is a dictionary of model field names mapped to a widget.

        ``localized_fields`` is a list of names of fields which should be localized.

        ``formfield_callback`` is a callable that takes a model field and returns
        a form field.

        ``labels`` is a dictionary of model field names mapped to a label.

        ``help_texts`` is a dictionary of model field names mapped to a help text.

        ``error_messages`` is a dictionary of model field names mapped to a
        dictionary of error messages.

        ``field_classes`` is a dictionary of model field names mapped to a form
        field class.
        """
        # Create the inner Meta class. FIXME: ideally, we should be able to
        # construct a ModelForm without creating and passing in a temporary
        # inner class.

        # Build up a list of attributes that the Meta object will have.
        attrs = {'model': model}
        if fields is not None:
            attrs['fields'] = fields
        if exclude is not None:
            attrs['exclude'] = exclude
        if widgets is not None:
            attrs['widgets'] = widgets
        if localized_fields is not None:
            attrs['localized_fields'] = localized_fields
        if labels is not None:
            attrs['labels'] = labels
        if help_texts is not None:
            attrs['help_texts'] = help_texts
        if error_messages is not None:
            attrs['error_messages'] = error_messages
        if field_classes is not None:
            attrs['field_classes'] = field_classes

        # If parent form class already has an inner Meta, the Meta we're
        # creating needs to inherit from the parent's inner meta.
        bases = (form.Meta,) if hasattr(form, 'Meta') else ()
        Meta = type('Meta', bases, attrs)
        if formfield_callback:
            Meta.formfield_callback = staticmethod(formfield_callback)
        # Give this new form class a reasonable name.
        class_name = model.__name__ + 'Form'

        # Class attributes for the new form class.
        form_class_attrs = {
            'Meta': Meta,
            'formfield_callback': formfield_callback
        }

        if (getattr(Meta, 'fields', None) is None and
                getattr(Meta, 'exclude', None) is None):
            raise ImproperlyConfigured(
                "Calling modelform_factory without defining 'fields' or "
                "'exclude' explicitly is prohibited."
            )

        # Instantiate type(form) in order to use the same metaclass as form.
        return type(form)(class_name, (form,), form_class_attrs)

    # ModelFormSets ##############################################################

    class BaseModelFormSet(BaseFormSet):
        """
        A ``FormSet`` for editing a queryset and/or adding new objects to it.
        """
        model = None

        # Set of fields that must be unique among forms of this set.
        unique_fields = set()

        def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
                     queryset=None, *, initial=None, **kwargs):
            self.queryset = queryset
            self.initial_extra = initial
            defaults = {'data': data, 'files': files, 'auto_id': auto_id, 'prefix': prefix}
            defaults.update(kwargs)
            super().__init__(**defaults)

        def initial_form_count(self):
            """Returns the number of forms that are required in this FormSet."""
            if not (self.data or self.files):
                return len(self.get_queryset())
            return super().initial_form_count()

        def _existing_object(self, pk):
            if not hasattr(self, '_object_dict'):
                self._object_dict = {o.pk: o for o in self.get_queryset()}
            return self._object_dict.get(pk)

        def _get_to_python(self, field):
            """
            If the field is a related field, fetch the concrete field's (that
            is, the ultimate pointed-to field's) to_python.
            """
            while field.remote_field is not None:
                field = field.remote_field.get_related_field()
            return field.to_python

        def _construct_form(self, i, **kwargs):
            if self.is_bound and i < self.initial_form_count():
                pk_key = "%s-%s" % (self.add_prefix(i), self.model._meta.pk.name)
                pk = self.data[pk_key]
                pk_field = self.model._meta.pk
                to_python = self._get_to_python(pk_field)
                pk = to_python(pk)
                kwargs['instance'] = self._existing_object(pk)
            if i < self.initial_form_count() and 'instance' not in kwargs:
                kwargs['instance'] = self.get_queryset()[i]
            if i >= self.initial_form_count() and self.initial_extra:
                # Set initial values for extra forms
                try:
                    kwargs['initial'] = self.initial_extra[i - self.initial_form_count()]
                except IndexError:
                    pass
            return super()._construct_form(i, **kwargs)

        def get_queryset(self):
            if not hasattr(self, '_queryset'):
                if self.queryset is not None:
                    qs = self.queryset
                else:
                    qs = self.model._default_manager.get_queryset()

                # If the queryset isn't already ordered we need to add an
                # artificial ordering here to make sure that all formsets
                # constructed from this queryset have the same form order.
                if not qs.ordered:
                    qs = qs.order_by(self.model._meta.pk.name)

                # Removed queryset limiting here. As per discussion re: #13023
                # on django-dev, max_num should not prevent existing
                # related objects/inlines from being displayed.
                self._queryset = qs
            return self._queryset

        def save_new(self, form, commit=True):
            """Saves and returns a new model instance for the given form."""
            return form.save(commit=commit)

        def save_existing(self, form, instance, commit=True):
            """Saves and returns an existing model instance for the given form."""
            return form.save(commit=commit)

        def delete_existing(self, obj, commit=True):
            """Deletes an existing model instance."""
            if commit:
                obj.delete()

        def save(self, commit=True):
            """Saves model instances for every form, adding and changing instances
            as necessary, and returns the list of instances.
            """
            if not commit:
                self.saved_forms = []

                def save_m2m():
                    for form in self.saved_forms:
                        form.save_m2m()
                self.save_m2m = save_m2m
            return self.save_existing_objects(commit) + self.save_new_objects(commit)

        save.alters_data = True

        def clean(self):
            self.validate_unique()

        def validate_unique(self):
            # Collect unique_checks and date_checks to run from all the forms.
            all_unique_checks = set()
            all_date_checks = set()
            forms_to_delete = self.deleted_forms
            valid_forms = [form for form in self.forms if form.is_valid() and form not in forms_to_delete]
            for form in valid_forms:
                exclude = form._get_validation_exclusions()
                unique_checks, date_checks = form.instance._get_unique_checks(exclude=exclude)
                all_unique_checks = all_unique_checks.union(set(unique_checks))
                all_date_checks = all_date_checks.union(set(date_checks))

            errors = []
            # Do each of the unique checks (unique and unique_together)
            for uclass, unique_check in all_unique_checks:
                seen_data = set()
                for form in valid_forms:
                    # Get the data for the set of fields that must be unique among the forms.
                    row_data = (
                        field if field in self.unique_fields else form.cleaned_data[field]
                        for field in unique_check if field in form.cleaned_data
                    )
                    # Reduce Model instances to their primary key values
                    row_data = tuple(d._get_pk_val() if hasattr(d, '_get_pk_val') else d
                                     for d in row_data)
                    if row_data and None not in row_data:
                        # if we've already seen it then we have a uniqueness failure
                        if row_data in seen_data:
                            # poke error messages into the right places and mark
                            # the form as invalid
                            errors.append(self.get_unique_error_message(unique_check))
                            form._errors[NON_FIELD_ERRORS] = self.error_class([self.get_form_error()])
                            # remove the data from the cleaned_data dict since it was invalid
                            for field in unique_check:
                                if field in form.cleaned_data:
                                    del form.cleaned_data[field]
                        # mark the data as seen
                        seen_data.add(row_data)
            # iterate over each of the date checks now
            for date_check in all_date_checks:
                seen_data = set()
                uclass, lookup, field, unique_for = date_check
                for form in valid_forms:
                    # see if we have data for both fields
                    if (form.cleaned_data and form.cleaned_data[field] is not None and
                            form.cleaned_data[unique_for] is not None):
                        # if it's a date lookup we need to get the data for all the fields
                        if lookup == 'date':
                            date = form.cleaned_data[unique_for]
                            date_data = (date.year, date.month, date.day)
                        # otherwise it's just the attribute on the date/datetime
                        # object
                        else:
                            date_data = (getattr(form.cleaned_data[unique_for], lookup),)
                        data = (form.cleaned_data[field],) + date_data
                        # if we've already seen it then we have a uniqueness failure
                        if data in seen_data:
                            # poke error messages into the right places and mark
                            # the form as invalid
                            errors.append(self.get_date_error_message(date_check))
                            form._errors[NON_FIELD_ERRORS] = self.error_class([self.get_form_error()])
                            # remove the data from the cleaned_data dict since it was invalid
                            del form.cleaned_data[field]
                        # mark the data as seen
                        seen_data.add(data)

            if errors:
                raise ValidationError(errors)

        def get_unique_error_message(self, unique_check):
            if len(unique_check) == 1:
                return gettext("Please correct the duplicate data for %(field)s.") % {
                    "field": unique_check[0],
                }
            else:
                return gettext("Please correct the duplicate data for %(field)s, which must be unique.") % {
                    "field": get_text_list(unique_check, _("and")),
                }

        def get_date_error_message(self, date_check):
            return gettext(
                "Please correct the duplicate data for %(field_name)s "
                "which must be unique for the %(lookup)s in %(date_field)s."
            ) % {
                'field_name': date_check[2],
                'date_field': date_check[3],
                'lookup': str(date_check[1]),
            }

        def get_form_error(self):
            return gettext("Please correct the duplicate values below.")

        def save_existing_objects(self, commit=True):
            self.changed_objects = []
            self.deleted_objects = []
            if not self.initial_forms:
                return []

            saved_instances = []
            forms_to_delete = self.deleted_forms
            for form in self.initial_forms:
                obj = form.instance
                # If the pk is None, it means either:
                # 1. The object is an unexpected empty model, created by invalid
                #    POST data such as an object outside the formset's queryset.
                # 2. The object was already deleted from the database.
                if obj.pk is None:
                    continue
                if form in forms_to_delete:
                    self.deleted_objects.append(obj)
                    self.delete_existing(obj, commit=commit)
                elif form.has_changed():
                    self.changed_objects.append((obj, form.changed_data))
                    saved_instances.append(self.save_existing(form, obj, commit=commit))
                    if not commit:
                        self.saved_forms.append(form)
            return saved_instances

        def save_new_objects(self, commit=True):
            self.new_objects = []
            for form in self.extra_forms:
                if not form.has_changed():
                    continue
                # If someone has marked an add form for deletion, don't save the
                # object.
                if self.can_delete and self._should_delete_form(form):
                    continue
                self.new_objects.append(self.save_new(form, commit=commit))
                if not commit:
                    self.saved_forms.append(form)
            return self.new_objects

        def add_fields(self, form, index):
            """Add a hidden field for the object's primary key."""
            from django.db.models import AutoField, OneToOneField, ForeignKey
            self._pk_field = pk = self.model._meta.pk
            # If a pk isn't editable, then it won't be on the form, so we need to
            # add it here so we can tell which object is which when we get the
            # data back. Generally, pk.editable should be false, but for some
            # reason, auto_created pk fields and AutoField's editable attribute is
            # True, so check for that as well.

            def pk_is_not_editable(pk):
                return (
                    (not pk.editable) or (pk.auto_created or isinstance(pk, AutoField)) or (
                        pk.remote_field and pk.remote_field.parent_link and
                        pk_is_not_editable(pk.remote_field.model._meta.pk)
                    )
                )
            if pk_is_not_editable(pk) or pk.name not in form.fields:
                if form.is_bound:
                    # If we're adding the related instance, ignore its primary key
                    # as it could be an auto-generated default which isn't actually
                    # in the database.
                    pk_value = None if form.instance._state.adding else form.instance.pk
                else:
                    try:
                        if index is not None:
                            pk_value = self.get_queryset()[index].pk
                        else:
                            pk_value = None
                    except IndexError:
                        pk_value = None
                if isinstance(pk, OneToOneField) or isinstance(pk, ForeignKey):
                    qs = pk.remote_field.model._default_manager.get_queryset()
                else:
                    qs = self.model._default_manager.get_queryset()
                qs = qs.using(form.instance._state.db)
                if form._meta.widgets:
                    widget = form._meta.widgets.get(self._pk_field.name, HiddenInput)
                else:
                    widget = HiddenInput
                form.fields[self._pk_field.name] = ModelChoiceField(qs, initial=pk_value, required=False, widget=widget)
            super().add_fields(form, index)

    def modelformset_factory(model, form=ModelForm, formfield_callback=None,
                             formset=BaseModelFormSet, extra=1, can_delete=False,
                             can_order=False, max_num=None, fields=None, exclude=None,
                             widgets=None, validate_max=False, localized_fields=None,
                             labels=None, help_texts=None, error_messages=None,
                             min_num=None, validate_min=False, field_classes=None):
        """
        Returns a FormSet class for the given Django model class.
        """
        meta = getattr(form, 'Meta', None)
        if (getattr(meta, 'fields', fields) is None and
                getattr(meta, 'exclude', exclude) is None):
            raise ImproperlyConfigured(
                "Calling modelformset_factory without defining 'fields' or "
                "'exclude' explicitly is prohibited."
            )

        form = modelform_factory(model, form=form, fields=fields, exclude=exclude,
                                 formfield_callback=formfield_callback,
                                 widgets=widgets, localized_fields=localized_fields,
                                 labels=labels, help_texts=help_texts,
                                 error_messages=error_messages, field_classes=field_classes)
        FormSet = formset_factory(form, formset, extra=extra, min_num=min_num, max_num=max_num,
                                  can_order=can_order, can_delete=can_delete,
                                  validate_min=validate_min, validate_max=validate_max)
        FormSet.model = model
        return FormSet

    # InlineFormSets #############################################################

    class BaseInlineFormSet(BaseModelFormSet):
        """A formset for child objects related to a parent."""
        def __init__(self, data=None, files=None, instance=None,
                     save_as_new=False, prefix=None, queryset=None, **kwargs):
            if instance is None:
                self.instance = self.fk.remote_field.model()
            else:
                self.instance = instance
            self.save_as_new = save_as_new
            if queryset is None:
                queryset = self.model._default_manager
            if self.instance.pk is not None:
                qs = queryset.filter(**{self.fk.name: self.instance})
            else:
                qs = queryset.none()
            self.unique_fields = {self.fk.name}
            super().__init__(data, files, prefix=prefix, queryset=qs, **kwargs)

            # Add the generated field to form._meta.fields if it's defined to make
            # sure validation isn't skipped on that field.
            if self.form._meta.fields and self.fk.name not in self.form._meta.fields:
                if isinstance(self.form._meta.fields, tuple):
                    self.form._meta.fields = list(self.form._meta.fields)
                self.form._meta.fields.append(self.fk.name)

        def initial_form_count(self):
            if self.save_as_new:
                return 0
            return super().initial_form_count()

        def _construct_form(self, i, **kwargs):
            form = super()._construct_form(i, **kwargs)
            if self.save_as_new:
                # Remove the primary key from the form's data, we are only
                # creating new instances
                form.data[form.add_prefix(self._pk_field.name)] = None

                # Remove the foreign key from the form's data
                form.data[form.add_prefix(self.fk.name)] = None

            # Set the fk value here so that the form can do its validation.
            fk_value = self.instance.pk
            if self.fk.remote_field.field_name != self.fk.remote_field.model._meta.pk.name:
                fk_value = getattr(self.instance, self.fk.remote_field.field_name)
                fk_value = getattr(fk_value, 'pk', fk_value)
            setattr(form.instance, self.fk.get_attname(), fk_value)
            return form

        @classmethod
        def get_default_prefix(cls):
            return cls.fk.remote_field.get_accessor_name(model=cls.model).replace('+', '')

        def save_new(self, form, commit=True):
            # Ensure the latest copy of the related instance is present on each
            # form (it may have been saved after the formset was originally
            # instantiated).
            setattr(form.instance, self.fk.name, self.instance)
            # Use commit=False so we can assign the parent key afterwards, then
            # save the object.
            obj = form.save(commit=False)
            pk_value = getattr(self.instance, self.fk.remote_field.field_name)
            setattr(obj, self.fk.get_attname(), getattr(pk_value, 'pk', pk_value))
            if commit:
                obj.save()
            # form.save_m2m() can be called via the formset later on if commit=False
            if commit and hasattr(form, 'save_m2m'):
                form.save_m2m()
            return obj

        def add_fields(self, form, index):
            super().add_fields(form, index)
            if self._pk_field == self.fk:
                name = self._pk_field.name
                kwargs = {'pk_field': True}
            else:
                # The foreign key field might not be on the form, so we poke at the
                # Model field to get the label, since we need that for error messages.
                name = self.fk.name
                kwargs = {
                    'label': getattr(form.fields.get(name), 'label', capfirst(self.fk.verbose_name))
                }
                if self.fk.remote_field.field_name != self.fk.remote_field.model._meta.pk.name:
                    kwargs['to_field'] = self.fk.remote_field.field_name

            # If we're adding a new object, ignore a parent's auto-generated key
            # as it will be regenerated on the save request.
            if self.instance._state.adding:
                if kwargs.get('to_field') is not None:
                    to_field = self.instance._meta.get_field(kwargs['to_field'])
                else:
                    to_field = self.instance._meta.pk
                if to_field.has_default():
                    setattr(self.instance, to_field.attname, None)

            form.fields[name] = InlineForeignKeyField(self.instance, **kwargs)

        def get_unique_error_message(self, unique_check):
            unique_check = [field for field in unique_check if field != self.fk.name]
            return super().get_unique_error_message(unique_check)

    def _get_foreign_key(parent_model, model, fk_name=None, can_fail=False):
        """
        Finds and returns the ForeignKey from model to parent if there is one
        (returns None if can_fail is True and no such field exists). If fk_name is
        provided, assume it is the name of the ForeignKey field. Unless can_fail is
        True, an exception is raised if there is no ForeignKey from model to
        parent_model.
        """
        # avoid circular import
        from django.db.models import ForeignKey
        opts = model._meta
        if fk_name:
            fks_to_parent = [f for f in opts.fields if f.name == fk_name]
            if len(fks_to_parent) == 1:
                fk = fks_to_parent[0]
                if not isinstance(fk, ForeignKey) or \
                        (fk.remote_field.model != parent_model and
                         fk.remote_field.model not in parent_model._meta.get_parent_list()):
                    raise ValueError(
                        "fk_name '%s' is not a ForeignKey to '%s'." % (fk_name, parent_model._meta.label)
                    )
            elif len(fks_to_parent) == 0:
                raise ValueError(
                    "'%s' has no field named '%s'." % (model._meta.label, fk_name)
                )
        else:
            # Try to discover what the ForeignKey from model to parent_model is
            fks_to_parent = [
                f for f in opts.fields
                if isinstance(f, ForeignKey) and (
                    f.remote_field.model == parent_model or
                    f.remote_field.model in parent_model._meta.get_parent_list()
                )
            ]
            if len(fks_to_parent) == 1:
                fk = fks_to_parent[0]
            elif len(fks_to_parent) == 0:
                if can_fail:
                    return
                raise ValueError(
                    "'%s' has no ForeignKey to '%s'." % (
                        model._meta.label,
                        parent_model._meta.label,
                    )
                )
            else:
                raise ValueError(
                    "'%s' has more than one ForeignKey to '%s'." % (
                        model._meta.label,
                        parent_model._meta.label,
                    )
                )
        return fk

    def inlineformset_factory(parent_model, model, form=ModelForm,
                              formset=BaseInlineFormSet, fk_name=None,
                              fields=None, exclude=None, extra=3, can_order=False,
                              can_delete=True, max_num=None, formfield_callback=None,
                              widgets=None, validate_max=False, localized_fields=None,
                              labels=None, help_texts=None, error_messages=None,
                              min_num=None, validate_min=False, field_classes=None):
        """
        Returns an ``InlineFormSet`` for the given kwargs.

        You must provide ``fk_name`` if ``model`` has more than one ``ForeignKey``
        to ``parent_model``.
        """
        fk = _get_foreign_key(parent_model, model, fk_name=fk_name)
        # enforce a max_num=1 when the foreign key to the parent model is unique.
        if fk.unique:
            max_num = 1
        kwargs = {
            'form': form,
            'formfield_callback': formfield_callback,
            'formset': formset,
            'extra': extra,
            'can_delete': can_delete,
            'can_order': can_order,
            'fields': fields,
            'exclude': exclude,
            'min_num': min_num,
            'max_num': max_num,
            'widgets': widgets,
            'validate_min': validate_min,
            'validate_max': validate_max,
            'localized_fields': localized_fields,
            'labels': labels,
            'help_texts': help_texts,
            'error_messages': error_messages,
            'field_classes': field_classes,
        }
        FormSet = modelformset_factory(model, **kwargs)
        FormSet.fk = fk
        return FormSet

    # Fields #####################################################################

    class InlineForeignKeyField(Field):
        """
        A basic integer field that deals with validating the given value to a
        given parent instance in an inline.
        """
        widget = HiddenInput
        default_error_messages = {
            'invalid_choice': _('The inline foreign key did not match the parent instance primary key.'),
        }

        def __init__(self, parent_instance, *args, pk_field=False, to_field=None, **kwargs):
            self.parent_instance = parent_instance
            self.pk_field = pk_field
            self.to_field = to_field
            if self.parent_instance is not None:
                if self.to_field:
                    kwargs["initial"] = getattr(self.parent_instance, self.to_field)
                else:
                    kwargs["initial"] = self.parent_instance.pk
            kwargs["required"] = False
            super().__init__(*args, **kwargs)

        def clean(self, value):
            if value in self.empty_values:
                if self.pk_field:
                    return None
                # if there is no value act as we did before.
                return self.parent_instance
            # ensure the we compare the values as equal types.
            if self.to_field:
                orig = getattr(self.parent_instance, self.to_field)
            else:
                orig = self.parent_instance.pk
            if force_text(value) != force_text(orig):
                raise ValidationError(self.error_messages['invalid_choice'], code='invalid_choice')
            return self.parent_instance

        def has_changed(self, initial, data):
            return False

    class ModelChoiceIterator:
        def __init__(self, field):
            self.field = field
            self.queryset = field.queryset

        def __iter__(self):
            if self.field.empty_label is not None:
                yield ("", self.field.empty_label)
            queryset = self.queryset.all()
            # Can't use iterator() when queryset uses prefetch_related()
            if not queryset._prefetch_related_lookups:
                queryset = queryset.iterator()
            for obj in queryset:
                yield self.choice(obj)

        def __len__(self):
            return (len(self.queryset) + (1 if self.field.empty_label is not None else 0))

        def choice(self, obj):
            return (self.field.prepare_value(obj), self.field.label_from_instance(obj))

    class ModelChoiceField(ChoiceField):
        """A ChoiceField whose choices are a model QuerySet."""
        # This class is a subclass of ChoiceField for purity, but it doesn't
        # actually use any of ChoiceField's implementation.
        default_error_messages = {
            'invalid_choice': _('Select a valid choice. That choice is not one of'
                                ' the available choices.'),
        }
        iterator = ModelChoiceIterator

        def __init__(self, queryset, empty_label="---------",
                     required=True, widget=None, label=None, initial=None,
                     help_text='', to_field_name=None, limit_choices_to=None,
                     *args, **kwargs):
            if required and (initial is not None):
                self.empty_label = None
            else:
                self.empty_label = empty_label

            # Call Field instead of ChoiceField __init__() because we don't need
            # ChoiceField.__init__().
            Field.__init__(self, required, widget, label, initial, help_text,
                           *args, **kwargs)
            self.queryset = queryset
            self.limit_choices_to = limit_choices_to   # limit the queryset later.
            self.to_field_name = to_field_name

        def get_limit_choices_to(self):
            """
            Returns ``limit_choices_to`` for this form field.

            If it is a callable, it will be invoked and the result will be
            returned.
            """
            if callable(self.limit_choices_to):
                return self.limit_choices_to()
            return self.limit_choices_to

        def __deepcopy__(self, memo):
            result = super(ChoiceField, self).__deepcopy__(memo)
            # Need to force a new ModelChoiceIterator to be created, bug #11183
            result.queryset = result.queryset
            return result

        def _get_queryset(self):
            return self._queryset

        def _set_queryset(self, queryset):
            self._queryset = queryset
            self.widget.choices = self.choices

        queryset = property(_get_queryset, _set_queryset)

        # this method will be used to create object labels by the QuerySetIterator.
        # Override it to customize the label.
        def label_from_instance(self, obj):
            """
            This method is used to convert objects into strings; it's used to
            generate the labels for the choices presented by this object. Subclasses
            can override this method to customize the display of the choices.
            """
            return force_text(obj)

        def _get_choices(self):
            # If self._choices is set, then somebody must have manually set
            # the property self.choices. In this case, just return self._choices.
            if hasattr(self, '_choices'):
                return self._choices

            # Otherwise, execute the QuerySet in self.queryset to determine the
            # choices dynamically. Return a fresh ModelChoiceIterator that has not been
            # consumed. Note that we're instantiating a new ModelChoiceIterator *each*
            # time _get_choices() is called (and, thus, each time self.choices is
            # accessed) so that we can ensure the QuerySet has not been consumed. This
            # construct might look complicated but it allows for lazy evaluation of
            # the queryset.
            return self.iterator(self)

        choices = property(_get_choices, ChoiceField._set_choices)

        def prepare_value(self, value):
            if hasattr(value, '_meta'):
                if self.to_field_name:
                    return value.serializable_value(self.to_field_name)
                else:
                    return value.pk
            return super().prepare_value(value)

        def to_python(self, value):
            if value in self.empty_values:
                return None
            try:
                key = self.to_field_name or 'pk'
                value = self.queryset.get(**{key: value})
            except (ValueError, TypeError, self.queryset.model.DoesNotExist):
                raise ValidationError(self.error_messages['invalid_choice'], code='invalid_choice')
            return value

        def validate(self, value):
            return Field.validate(self, value)

        def has_changed(self, initial, data):
            initial_value = initial if initial is not None else ''
            data_value = data if data is not None else ''
            return force_text(self.prepare_value(initial_value)) != force_text(data_value)

    class ModelMultipleChoiceField(ModelChoiceField):
        """A MultipleChoiceField whose choices are a model QuerySet."""
        widget = SelectMultiple
        hidden_widget = MultipleHiddenInput
        default_error_messages = {
            'list': _('Enter a list of values.'),
            'invalid_choice': _('Select a valid choice. %(value)s is not one of the'
                                ' available choices.'),
            'invalid_pk_value': _('"%(pk)s" is not a valid value for a primary key.')
        }

        def __init__(self, queryset, required=True, widget=None, label=None,
                     initial=None, help_text='', *args, **kwargs):
            super().__init__(
                queryset, None, required, widget, label, initial, help_text,
                *args, **kwargs
            )

        def to_python(self, value):
            if not value:
                return []
            return list(self._check_values(value))

        def clean(self, value):
            value = self.prepare_value(value)
            if self.required and not value:
                raise ValidationError(self.error_messages['required'], code='required')
            elif not self.required and not value:
                return self.queryset.none()
            if not isinstance(value, (list, tuple)):
                raise ValidationError(self.error_messages['list'], code='list')
            qs = self._check_values(value)
            # Since this overrides the inherited ModelChoiceField.clean
            # we run custom validators here
            self.run_validators(value)
            return qs

        def _check_values(self, value):
            """
            Given a list of possible PK values, returns a QuerySet of the
            corresponding objects. Raises a ValidationError if a given value is
            invalid (not a valid PK, not in the queryset, etc.)
            """
            key = self.to_field_name or 'pk'
            # deduplicate given values to avoid creating many querysets or
            # requiring the database backend deduplicate efficiently.
            try:
                value = frozenset(value)
            except TypeError:
                # list of lists isn't hashable, for example
                raise ValidationError(
                    self.error_messages['list'],
                    code='list',
                )
            for pk in value:
                try:
                    self.queryset.filter(**{key: pk})
                except (ValueError, TypeError):
                    raise ValidationError(
                        self.error_messages['invalid_pk_value'],
                        code='invalid_pk_value',
                        params={'pk': pk},
                    )
            qs = self.queryset.filter(**{'%s__in' % key: value})
            pks = set(force_text(getattr(o, key)) for o in qs)
            for val in value:
                if force_text(val) not in pks:
                    raise ValidationError(
                        self.error_messages['invalid_choice'],
                        code='invalid_choice',
                        params={'value': val},
                    )
            return qs

        def prepare_value(self, value):
            if (hasattr(value, '__iter__') and
                    not isinstance(value, str) and
                    not hasattr(value, '_meta')):
                return [super(ModelMultipleChoiceField, self).prepare_value(v) for v in value]
            return super().prepare_value(value)

        def has_changed(self, initial, data):
            if initial is None:
                initial = []
            if data is None:
                data = []
            if len(initial) != len(data):
                return True
            initial_set = set(force_text(value) for value in self.prepare_value(initial))
            data_set = set(force_text(value) for value in data)
            return data_set != initial_set

    def modelform_defines_fields(form_class):
        return (form_class is not None and (
                hasattr(form_class, '_meta') and
                (form_class._meta.fields is not None or
                 form_class._meta.exclude is not None)
                ))